1. Field of the Invention
The present invention particularly relates to a method of manufacturing a long spline shaft which constitutes a propeller shaft for an automobile.
2. Description of the Prior Art
Conventionally, the following method has been adopted to manufacture a long spline shaft. Specifically, a solid stock is hot-forged to form a rough shape from which to form splines, and after the solid blank formed into the rough shape is cut, a spline portion is worked by a hobbing machine. Then, the root strength of the spline portion is increased by induction hardening.
The conventional manufacturing method using the aforesaid machining has the problems of a long working time and low productivity because general spline shafts are long. In addition, to impart sufficient strength to the roots of a splines, it is necessary to use a solid stock and induction hardening.
Although there is a method of forming splines by cold forging, there is a risk of buckling.
The present invention is intended to reduce the weight of a spline shaft by using a hollow stock, to prevent buckling during the formation of splines by omitting softening following ironing by using cold forging and to improve productivity by omitting induction hardening, as well as to provide a spline shaft having sufficient strength.
The present invention provides a method of manufacturing a spline shaft, which comprises ironing a hollow stock by cold forging and forming splines in a desired portion of the hollow stock by cold forging by using its work hardening.
Specifically, the present invention makes it possible to reduce the weight of a product by using a hollow stock, and to prevent buckling of the material of the hollow stock by bringing the entire hollow stock into a work-hardened state by ironing it by cold forging before formation of splines and then forming a spline portion by cold forging without performing softening, as well as to obtain a predetermined root strength without requiring induction hardening. Accordingly, a reduction in weight is achieved, and the production speed and yield are improved.
The present invention is mainly directed to a long spline shaft for a propeller shaft of an automobile, and can also be applied to spline shafts for other machines which need transmission of power through a large area, such as airplane components, ship components, construction machinery and agricultural machinery.